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Marketable Investment Securities - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified | Dec. 31, 2014 | Jun. 30, 2014
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Schedule of Available-for-sale Securities [Line Items] |  |
Estimated fair value | $ 229,553 us-gaap_AvailableForSaleSecurities | $ 270,586 us-gaap_AvailableForSaleSecurities
Restricted Cash |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Estimated fair value | $ 22,138 us-gaap_AvailableForSaleSecurities / us-gaap_InvestmentTypeAxis = mygn_RestrictedCashMember |

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- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562 + Details
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Namespace Prefix: | us-gaap_
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- Details
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Namespace Prefix: | us-gaap_
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Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |